As is well known, an ionization chamber type X-ray detector of a computor tomograph has a structure shown in FIG. 4. Namely, the X-ray detector includes, within a sealed casing in which an xenon gas, etc., are enclosed, an array of electrode plates 34 of a plurality of signal electrode plates 3 (hereinafter referred to as the anode) and a plurality of bias electrode plates 4 (hereinafter referred to as the cathodes) which are alternately disposed parallel to the direction of the arrow 5 in which a fan beam X-ray enters. The front 2 of the casing 1 has an X-ray entrance window made of a material, highly transparent to X-rays, for example, of a thin aluminum film. The casing 1 has an arcuate shape with the X-ray entrance window on its inner side. The anode 3 are individually connected to current sensors circuit (not shown) while all the cathodes 4 are connected together to the output terminal of a direct current power source (not shown).
The array of electrode plates 34 in such an ionization chamber type X-ray detector has a structure such as that shown in FIG. 5. FIG. 5 shows the array of electrode plates 34 in a cross-sectional view taken along the arcuation of the X-ray detector. As shown in FIG. 5, the anode 3 and cathodes 4 are bonded, for example, by an epoxy bond 7 between two insulator support plates 6, for example, of ceramic.
In manufacturing such array of electrode plates 34, an electrode plate arranging jig is used in order to arrange anode 3 and cathodes 4 properly. The jig has an inner member which has a curved surface along the inner side of the finished arcuation of the array of electrode plates 34, the curved surface having thereon a plurality of grooves cut to pitches at which the electrode plates are arranged, and an outer member having a curved surface along the outer side of the finished arcuation of the array of electrode plates 34, the curved surface having a plurality of grooves cut to pitches at which the electrode plates are arranged, with the curved surfaces opposing at a predetermined spacing.
A predetermined arrangement of the electrode plates is obtained by inserting anode 3 and cathodes 4 alternately into the grooves cut on the two opposing curved surfaces of a jig such as that mentioned above in the space between the curved surfaces. Under this condition, an insulator support plate 6 is bonded to each of the upper and lower ends of the row of electrode plates to form the array of electrode plates 34. The jig is removed from the array of electrode plates 34 after the bond is completely hardened.
Preferably, the width of each of the electrode insertion grooves in the jig is as close as possible to each electrode plate in order to enhance the accuracy with which the electrode plates are arranged. However, in order to facilitate the work of inserting electrode plates having variations in thickness and the work of removing the jig from the arcuate finished array of electrode plates 34, it is necessary that the groove width has proper leeway compared to the thickness of the electrode plates. Thus, the prior art jig does not necessarily provide a satisfactory precision with which the electrodes are arranged.